The present technology relates to an electrostatic charger for charging to a uniform potential the peripheral surface of the photosensitive body of an apparatus for electrophotographic image formation.
An apparatus for electrophotographic image formation includes a photosensitive body and an electrostatic charger for charging the peripheral surface of the body to a uniform potential. The charger may be a noncontact charger out of contact with the photosensitive body. The noncontact charger includes an electrode. Application of high voltage to the electrode causes the electrode to discharge so as to charge the peripheral surface of the photosensitive body.
The charger electrode may be a needle electrode with needles. The needles extend toward the peripheral surface of the photosensitive body and are arrayed perpendicularly to the direction in which the surface moves. The portions of the needles which generate a high-voltage electric field attract ambient dust. Large amounts of dust on the needles prevent them from discharging properly.
JP-H11-338265A discloses a conventional electrostatic charger, which includes a needle electrode and a pair of pads supported on both sides of the needle array of the electrode. Movement of the pads along the needle array brings them into contact with the needles in order so as to remove dust from the needles.
The charger pads are made of felt or the like, so that they are not sufficiently elastic. This makes the tips of the electrode needles liable to deform. If the pads are made of felt, the felt fibers cut by the contact of the pads with the needles may stick to the needles. The pads come into contact with the sides of the needles which are parallel with the needle array. This makes it impossible to reliably clean the overall surfaces of the needle tips, to which the generation of a high-voltage electric field makes dust most liable to stick.
The assignee of this patent application has proposed an image forming apparatus including a photosensitive body and an electrostatic charger, which includes a needle electrode and a cleaning member. The electrode has an array of needles each extending toward the peripheral surface of the photosensitive body. The cleaning member is supported movably along the needle array between the electrode and the surface of the photosensitive body. While the cleaning member is moving along the needle array, the needle tips sink in order in the peripheral surface of the cleaning member and subsequently move out of it. This brings the overall surfaces of the needle tips into contact with the cleaning member so as to clean them reliably without deforming the needles and causing fibers to stick to the needles.
The cleaning member may include a roller and a shaft. The roller has a bore formed through it, in which the shaft is press-fitted. In this case, if the environment in which the electrostatic charger is used changes, or if the charger is used for a long time, the roller may crack when the cleaning member moves. If the roller cracks, the efficiency at which the electrode needles are cleaned decreases, and frequent replacement of the cleaning member decreases the efficiency of image formation of the apparatus, so that the apparatus cost rises.